The invention generally relates to a method for limiting endstop collisions in semi-active seat suspension systems, and more particularly the invention relates to a method for limiting endstop collisions by adjusting the seat damping gain when either the system exceeds an endstop detection threshold or the seat is leveled outside of a normal leveling limits.
In semi-active control systems, such as semi-active seat suspensions for example, the seat displacement control force provided to the system by a damper is continually adjusted in response to system inputs to provide isolation of high frequency low amplitude disturbances and to also improve performance of the seat suspension and comfort to the rider by limiting endstop collisions. An end stop collision occurs when the mechanical system in which the damper is connected hits the end stop, for example the maximum mechanical limits of the extension and/or rebound strokes when a sufficient transient load is encountered. If the system velocity is high enough when the end stop collision occurs, a very rapid impact results. The bottoming and topping out at an end stop condition imparts unwanted stresses to the mechanical components in the system and such collisions can be an annoyance to the driver. More significantly, when a driver or other seat occupant experiences endstop collisions, such collisions can effect the physical health of the seat occupant.
Prior art semi-active control systems include a control routine that serves to provide a damping force that is proportional to the relative velocity of the seat or of another component of the seat suspension system. U.S. Pat. Nos. 5,276,622 and 4,821,849 illustrate prior art semi-active control systems. In many situations the tuning values applied to the system by the control routines are selected to control the suspended seat over an expected or typical range of inputs, rider weights, etc. These selected tuning values are unique for each system and are selected based on the particular damper design, installation kinematics, and control system being used. In this way known semi-active systems have attempted to provide the appropriate magnitude of damping forces in response to typical inputs to limit endstop collisions. Because known semi-active systems are tuned for typical system inputs, when very large inputs outside the typical input range are encountered, the large inputs can still produce endstop collisions.
It is not practical to use prior art systems and methods to tune a control system so that the system is able to sufficiently damp the complete range of possible inputs to the seat suspension. A system tuned for the complete range of system inputs would be very heavy and expensive and would likely not meet the space, weight and cost restrictions for the suspension. Additionally, tuning a system for the complete range of possible inputs including large inputs would degrade the ride over the routine or typical inputs. Finally, when endstop collisions occur, the collisions typically are unabated in known prior art systems, and as a result, the suspension system may experience one or more additional endstop collisions. Such endstop collisions are referred to by those skilled in the art as rebounds.
Frequently, seat riders set their leveled seat height at an extremely high or low position proximate the respective upper or lower mechanical seat endstops. When the seat is set proximate the upper and lower endstops and an input is experienced, the system does not have sufficient time and distance to apply sufficient damping force to prevent endstop collisions. As a result, unintended and undesirable impacts with the mechanical endstops occur. Because the seat is proximate the mechanical endstops, the unintended and undesirable collisions occur even when a typical input is applied to the system.
The foregoing illustrates limitations known to exist in present semi-active devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to providing a large damping force in response to a non-typically large input and also provides the best overall ride quality and protection of the rider when the leveled seat height exceeds normal bounds. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
This is accomplished by the present invention which generally relates to a method for limiting endstop collisions in semi-active seat suspension systems, and more particularly the invention relates to a method for limiting endstop collisions by adjusting the damping gain factor when either the system exceeds an endstop detection threshold or the seat is leveled outside of normal leveling limits. Generally the seat suspension includes a first endstop limit, a second endstop limit and means for controlling the seat displacement, and the method for limiting endstop collisions comprises the steps of: sensing the position of the seat; determining the seat velocity; calculating a control signal by multiplying the seat velocity by a gain factor; and transmitting the control signal to said displacement control means to increase the damping to the required level.
More specifically in one aspect of the present invention, endstop collisions are limited by providing a temporary or transient control method referred to as rebound control which causes a large damping force to be applied by the seat suspension system in response to non-typically large inputs which cause the seat to cross or exceed an endstop detection threshold.
In another specific aspect of the invention, this is accomplished by providing a level control algorithm that provides additional level control when the seat is leveled outside the normal leveling zone. The degree of additional level control or gain factor supplied is a function of the distance the seat exceeds the normal leveling zone. In this aspect of the present invention, rider protection from end stop collisions is maximized.
The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures.